1 / 23

Photons @ RHIC: Results from STAR

Photons @ RHIC: Results from STAR. Marcia Maria de Moura for the STAR Collaboration. STAR Experiment At RHIC. Magnet. Time Projection Chamber. Coils. Silicon Tracker SVT & SSD. TPC Endcap & MWPC. FTPCs. Beam Beam Counters. Endcap Calorimeter. Central Trigger Barrel & TOF.

nolen
Download Presentation

Photons @ RHIC: Results from STAR

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Photons @ RHIC:Results from STAR Marcia Maria de Moura for the STAR Collaboration

  2. STAR Experiment At RHIC Magnet Time Projection Chamber Coils Silicon Tracker SVT & SSD TPC Endcap & MWPC FTPCs Beam Beam Counters Endcap Calorimeter Central Trigger Barrel & TOF Barrel EM Calorimeter PMD Marcia Maria de Moura

  3. Introduction Photons in A+A collisions • Mainly, from p0 , h decays • Important probe in many aspects • In STAR, allow better statistics to higher pT than charged pions • Direct photons • Main advantage – large mean free path in the created matter • Produced in all stages of the collision • thermal photons – access to temperature (initial, hadronization) • High pT photons to investigate hadron supression in A+A collisions • Extraction of direct photon production is harder due to large hadronic decay background → p0 (h) measurements very important Marcia Maria de Moura

  4. Inclusive g and p0 from the STAR TPC Measurement obtained from g conversion in TPC Material used as g converter: • Beampipe • SVT • SSD • Inner field cage • TPC gas Efficiency • g ~ 2% • p0 ~ 0.04% Marcia Maria de Moura

  5. g reconstruction • e+and e-are selected through dE/dx • loose cuts are applied • low pT accepted only if they do not come from collision vertex • For the pairs, it is required a small opening angle and conversion vertex different from collision vertex • Trajectory of reconstructed g points back to collision vertex Marcia Maria de Moura

  6. Au+Au collisions at √sNN = 62.4 GeV - g spectra Centrality dependence • Curves are power law fits g and p0– Au+Au at 130 GeV J. Adams et al., Phys. Rev. C 70 (2004) 044902 • Error bars: statistical only • Systematic uncertainty: 20% • Combinatorial background has been subtracted • Other contributions, such as L decays, were verified to be negligible Marcia Maria de Moura

  7. Au+Au collisions at √sNN = 62.4 GeV -p0 spectrum • Each point is the gaussian fit of the 2g invariant mass distribution for a given pT • ~10 MeV width, depending on pT • Systematic uncertainty of 30% Comparison of p0 to p+ and p- from STAR TPC dE/dx and TOFr shows good agreement. Marcia Maria de Moura

  8. Correlation of large ET photons with charged particles • Jet studies allow further investigation of parton energy loss mechanism • 2 particle correlations • probe of intra-jet (same side) and back-to-back jet (away side) • Previous studies • charged particle correlations for pT < 6 GeV/c • This Analysis • g (mostly from p0) – h+ correlations • Extends correlation energy range, due to EMC measurement of photons trigger  0 incoming partons associated h Marcia Maria de Moura

  9. d+Au collisions at √sNN=200 GeV • Data set • 3.9 M High Tower triggered events • EMC patch - 4 x 4 towers • High tower trigger - tower in a patch with the highest energy above threshold EMC Tower dh x df =0.05 x 0.05 • Selections and Cuts • Highest tower energy selected • Isolation cut • No track pointing in a 3 x 3 tower patch around main tower • Associated track – basic selection criterium used in many STAR analysis Marcia Maria de Moura

  10. d+Au correlations STAR preliminary STAR preliminary pTassociateddependence Etrigdependence Marcia Maria de Moura

  11. Jet properties – <jT > and √<kTrms > • jT - transverse momentum component of jet from jet axis • kT - transverse momentum component of initialparton Correlation (Gaussian) widths • sN→ near side • sF→ far side • ET → Etrig , • pT → pTassociated • < z > → fragmentation function of trigger photon (0.6~0.8) Marcia Maria de Moura

  12. Centrality dependence of sN and sF Preliminary No strong centrality dependence of either near and far side widths within errors Marcia Maria de Moura

  13. <jT > and √<kTrms > dependences Preliminary Increase of jT with pTassociated kT is smaler for larger pTassociated jT almost constant with ET. kT is larger for larger ET Marcia Maria de Moura

  14. First Results from Photon Multiplicity Detector • Two planes CPV+Pre-shower • Gas (Ar+CO2) detector of 82944 hexagonal cells • Detector area: 4.2 m2 • Distance from vertex: 5.4 m • -3.8 < h < -2.3 and full azimuthal coverage The CPV plane was not in present analysis Marcia Maria de Moura

  15. Photon Multiplicity Distribution Minimum Bias Au+Au @ 62.4 GeV dNg/dh # events h Ng • Ng at forward rapidities scales with Npart • Better agreement to data of AMPT model than HIJING Ng/0.5Npart Npart Marcia Maria de Moura

  16. Limiting Fragmentation trend Energy dependence Centrality dependence h - ybeam h - ybeam • No centrality dependence of limiting fragmentation for photons, unlike for charged particles • Photons undergo limiting fragmentation Marcia Maria de Moura

  17. Limiting Fragmentation Scenario for p and g • p production follows the LF scenario • Photon production is scaled down by about 7% to reflect the contribution from p0 dN/dh / 0.5 Npart y - ybeam nucl-ex/0502008 - Submited to PRL Marcia Maria de Moura

  18. Direct Photon measurements for p+p and d+Au • EMC measurements • Tower + SMD + pre-shower • p+p and d+Au, towards Au+Au • Direct photon spectra • Subtraction of background and contamination from inclusive spectra • p0, h photon decays • other neutral contribution (n,K0) • Contamination from charged hadrons • Acceptance/Efficiency corrections Marcia Maria de Moura

  19. Direct Photon Analysis Status • Systematic studies of BEMC/BSMD • Shower properties studies on BSMD • Cluster size, energy • Development of cluster algorhytm • Acceptance/efficiency • d+Au p0 embedded data • EMC module • Tower • (Dh, Df) = (0.05, 0.05) • dE/E ~ 16%/√E(GeV) • BMSD • (Dh, Df) strip= (0.007, 0.007) • sh= 2.4 mm + 5.6 mm /√E(GeV) • sf= 3.2 mm + 5.8 mm /√E(GeV) preliminary Marcia Maria de Moura

  20. p0 spectrum for d+Au collisions From EMC measurements Mass = 135±1 MeV Width = 28±0.6 MeV Event mixing nucl-ex/0412045 – to be published in Eur. Phys. J. C. • Reasonable agreement with pQCD calculations within errors Marcia Maria de Moura

  21. More to come... • Photon HBT (Jack Sandweiss talk) • Analysis of qinvariant photon pairs distribution • HBT peak produced by direct photons • Investigation of spatial and temporal dimensions of QGP phase • g-charged correlations in Au+Au • Potencial observation of away-side correlation from direct photons due to hadron (po) suppression • Investigation of parton energy loss PYTHIA Marcia Maria de Moura

  22. Back up slides Marcia Maria de Moura

  23. Near and Far side widths Decrease with increasing Etrig Decrease with increasing pTassociated Marcia Maria de Moura

More Related